This invention generally relates to a printer mechanism for producing indicia on a web medium including alphanumeric characters and symbols by suitable means, such as dot matrix characters. More particularly, the printer mechanism is an electronic type having a printhead assembly comprising a thermal printhead supported by a carrier member for traversing movement along a rotating operating shaft in printing a line of characters. The printhead assembly is then returned to its original starting position with the web medium being advanced one line to repeat the traversing movement of the carrier member and the printhead supported thereby in printing a subsequent line of characters. In one specific aspect, the electronic printer mechanism may comprise a peripheral printer component for use with a calculator or other data-processing unit so as to provide a printing capability therefor.
Heretofore, electronic printer mechanisms employed as printer peripherals for use with data-processing devices, such as calculators and computers, for example, have been characterized by the presence of many mechanical parts subject to maintenance and repair at frequent intervals. In addition, the presence of so many parts accompanied by space limitations within the housing of the printer mechanism have contributed to a tedious and time-consuming effort when the internal printer assembly must be disassembled for repair and/or replacement of parts.
Another area of difficulty experienced with electronic printer mechanisms lies in the mechanical structure employed to advance the paper upon completion of the printing of a line of characters so that subsequent lines of characters may be printed in an orderly manner. Mechanical paper-advancing mechanisms included in electronic printers, especially those which are subject to high speed requirements, are prone to jamming, either because of the limited tolerances built thereinto with respect to alignment of the paper and precise one-line advancement at a time or because of careless handling by operators in initially positioning the paper or in removing same from the printer mechanism.
Typical of the type of electronic printer mechanisms with which the present invention is concerned is the electronic printer disclosed in U.S. Pat. No. 3,874,493 Boyd issued Apr. 1, 1975 in which a thermal printhead is supported on a carriage member for traversing movement along a pair of guide rods to enable the thermal printhead by selective actuation of the semiconductor mesas thereof to produce a line of printed characters upon paper. The paper is interposed between the printhead and a pressure pad supported by a pressure pad carriage moving along a track in unison with the thermal printhead. U.S. Pat. No. 3,874,493 Boyd is hereby incorporated by reference.